My heater works good when im driving but i noticed when im parked for awhile such as drive thru waiting for munchies it starts blowing cold air, then as soon as i get going on the road again it blows hot air. Could it be the heater core going out, any ideas appreciated.

 

I heard from a couple of people that ford messed up on the defrost function that it is also turns on the A/C if that makes some sort of sense. Whether it's on heat or not.